1. Field of the Invention
This invention relates generally to a control valve for the control of a hydraulic consumer, independently of the load, having a distributing slide valve to control the direction of movement and the speed of movement of the consumer and a throttle valve associated with the distributing slide valve which, when a pump is connected with the consumer, can be pressurized toward an open position by the pressure downstream of a throttle point of the distributing slide valve and toward a closed position by the load pressure of the consumer and by a spring.
2. Description of the Currently Available Technology
Control valves with an associated throttle valve, for example, a pressure balance, are used in load-sensing drive systems. When a pump is connected with the consumer, for example, to lift a load that is being exerted on a hydraulic cylinder, these control valves control the speed of movement specified by the aperture width of the control valve, regardless of the load that is being exerted on the consumer. In this case, for example, the throttle valve is located downstream of the control valve and is pressurized in the closing direction by the force of a spring and by the load pressure being exerted on the consumer and is pressurized in the opening direction by the pressure downstream of the throttle point of the control valve. When the consumer is connected to the pump, the pressure differential at the control valve is kept constant by the throttle valve, even when the load pressure of the consumer varies. As a result of which, the quantity of hydraulic fluid flowing from the pump to the consumer remains constant and the speed of movement specified by the aperture width of the distributing slide valve is kept constant.
When the consumer is connected with a reservoir, for example, to lower a load that is being supported by a hydraulic cylinder, the speed of movement is also specified by the aperture width of the control valve. The pressure in the control pressure chamber of the throttle valve that acts toward the closed position is thereby relieved toward the reservoir so that the throttle valve is pressurized into the open position by the pressure downstream of the throttle point of the control valve. Consequently, the quantity of hydraulic fluid flowing from the consumer to the reservoir through the throttle point of the control valve is a function of the load being supported by the consumer. However, and in particular with loads that are exerted in the discharge direction, such as loads that are suspended on hydraulic cylinders, for example, it is necessary to restrict the quantity of hydraulic fluid flowing out of the consumer and thus to limit the speed of descent of the consumer.
To limit the speed of movement of the consumer when the consumer is connected to the reservoir by means of the control valve, the prior art provides additional valves to achieve a control of the quantity of hydraulic fluid discharged from the consumer independently of the load, and thus to control the speed of movement of the consumer in the discharge direction. For this purpose, flow regulators or descent braking valves are used to restrict the speed of descent on hydraulic cylinders, in particular for suspended loads. The prior art also includes the use of throttle valves, in particular throttle screws, to restrict the speed of descent. However, these throttle valves act as a function of the load. On propulsion motors, the prior art provides propulsion braking valves in addition to the control valves to restrict the quantity of hydraulic fluid flowing out, whereby these braking valves bank up a brake pressure in the discharge side of the propulsion motor, for example, if the truck driven by the propulsion motor is traveling downhill.
It is an object of the invention to provide a control valve that makes it possible to easily and economically restrict the quantity of hydraulic fluid flowing out of a consumer to a reservoir, and thus to control the speed of movement of the consumer in the discharge direction independently of the load being exerted on the consumer.